The proposed studies are designed to obtain further information relating to the influence of gonadal steroid hormones on secretory patterns of prolactin, growth hormone and thyrotropin, and the neuroendocrine regulation of these pituitary hormones in sheep. Preliminary investigations in our laboratory have indicated that the secretion of prolactin, GH and, to a lesser extent, TSH occurs in an episodic manner. It is our intention to further define these episodic secretory patterns and examine the influence of gonadal steroid hormones on their frequency and magnitude. Additionally the influence of somatostatin on frequency and magnitude of GH secretory spikes will be examined.